Surgical Access System and Related Methods

ABSTRACT

A surgical access system comprising a tissue dilation assembly and a tissue retraction assembly, both of which may be equipped with one or more electrodes for use in detecting the existence of (and optionally the distance and/or direction to) neural structures.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/821,224, filed on 27 Jan. 2014 (pending); U.S. patent applicationSer. No. 13/821,224 is a national stage of International Pat. App. No.PCT/US11/01489, filed on 23 Aug. 2011 (abandoned); International Pat.App. No. PCT/US11/01489 claims priority to U.S. Pat. App. No. 61/376,163filed Aug. 23, 2010 (expired), Pat. App. No. 61/390,248 filed Oct. 6,2010 (expired), and Pat. App. No. 61/473,138 filed Apr. 22, 2011(expired). The complete disclosures of each of the foregoing are herebyincorporated by reference into this application as if set forth fullyherein.

FIELD

This disclosure relates to a surgical retraction system and relatedinstrumentation and methods for accessing a surgical target site for thepurpose of performing surgical procedures.

BACKGROUND

A noteworthy trend in the medical community is the move away fromperforming surgery via traditional “open” techniques in favor ofminimally invasive or minimal access techniques. Open surgicaltechniques are generally undesirable in that they typically requirelarge incisions and high amounts of tissue displacement to gain accessto the surgical target site, which produces concomitantly high amountsof pain, lengthened hospitalization (increasing health care costs), andhigh morbidity in the patient population. Less-invasive surgicaltechniques (including so-called “minimal access” and “minimallyinvasive” techniques) are gaining favor due to the fact that theyinvolve accessing the surgical target site via incisions ofsubstantially smaller size with greatly reduced tissue displacementrequirements. This, in turn, reduces the pain, morbidity and costassociated with such procedures. On such minimally invasive approach, alateral trans-psoas approach to the spine, developed by NuVasive®, Inc.,San Diego, Calif. (XLIF®) has demonstrated great success in reducingpatient morbidity, shortening the length of hospitalization and fastrecovery time when it is employed. Improvement of instruments andmethods employed to the during the lateral access has the potential tofurther reduce operative time, expand applications for the lateralapproach, and increase surgeon adoption of the procedure, all of whichwill ultimately benefit the patient by provide more opportunity forminimally invasive surgical correction of their ailments. Theinstruments and methods described herein are designed to address theseneeds, among others.

SUMMARY

The present application describes systems and methods for performingsurgical procedures on the spine, including (according to a preferredmethod) creating an operative corridor to the spine via a substantiallylateral, trans-psoas approach. The access described herein isaccomplished with a surgical access system including a dilation assemblyand a retraction assembly. To create the lateral access corridor to thelumbar spine, the patient is positioned on their side and the surgicalaccess system is advanced through an incision, into the retroperitonealspace, and then through the psoas muscle until the targeted spinal site(e.g. the disc space between a pair of adjacent vertebral bodies) isreached. The access system may include a sequential dilation system ofincreasing diameter and a tissue retractor assembly. The sequentialdilation assembly is advanced to the target site first and the retractorassembly is then advanced to the target site over the sequentialdilation system. Nerve monitoring may be performed while advancing eachof the dilation system and retraction system to the target site todetect the presence of, and thereby avoid, nerves lying in thetrans-psoas path to the target site.

The retractor assembly includes a plurality of retractor blades, threeaccording to a preferred embodiment, and a body. The retractor assemblyis then operated to expand the operative corridor to the desiredgeometry and dimension. The body includes two arms connected to eachother by a pivot. Handle extenders may be attached to the arms andsqueezed to cause the cephalad-most and caudal most arms to move awayfrom each other and away from the posterior blade (which may preferablybe fixed in position) to expand the operative corridor anteriorly (awayfrom the nerves posterior to the posterior blade). The cephalad-most andcaudal-most blades may also pivot or splay outward from a central axisof insertion to expand the operative corridor at the surgical sitewithout increasing the size of the incision. The retractor assemblyexhibits continuous splay such that splay to any angle (within apredetermined range) may be achieved. The continuous splay is achievedthrough the use of a gear mechanism coupled to each arm of the retractorbody. The gear mechanism may be a lead screw driven rack and piniongear. The rack may translate vertically in the retractor body causingthe pinion to rotate. The pinion is connected to one end of a rotatingarm which is coupled at the opposite end to one of the retractor bladesto be splayed. Each of the two gear mechanisms (one for each arm of theretractor) operates independently such that the blades can be adjustedindependent of each other.

According to one example, the posterior most of the blades may be fixedin position relative to the spine prior to operating the retractor toopen the blades. This may be accomplished, for example, by attaching aninterdiscal shim to the blade and inserting the distal end of the shiminto the disc space. Alternatively, or in addition, this may beaccomplished by connecting an articulating arm between the surgicaltable (or other suitable mount) and posterior blade (via a translatingarm to which the posterior blade is attached). In this manner, theposterior blade will not move posteriorly towards nerve tissue locatedin the posterior portion of the psoas muscle. Instead, the remainingblades and will move away from the posterior blade to expand the accesscorridor. In addition to the interdiscal shim, blade extenders may becoupled to the cephalad and caudal blades. The extenders may havecontoured distal ends to match the anatomy at the anterior of thevertebral body.

The retractor assembly may be configured to employ a supplementalanterior retractor blade. The supplemental anterior retractor bladeprovides for selectively increasing the number of retractor bladesforming the operative corridor during (or before) use and prevent tissuecreep into the operative corridor from the anterior border. The abilityto selectively increase the number of retractor blades affordsadditional user control over the size and/or configuration of the accesscorridor, advantageously increasing the versatility of retractorassembly. The supplemental anterior retractor blade includes a blade anda handle. A connecting device cooperates with the supplemental blade andthe cephalad and caudal blades to hold the supplemental retractor bladein position. The supplemental retractor blade may be manipulated tomanually retract tissue anteriorly. Thereafter the connecting elementmay be engaged to the retractor blades to hold the supplemental blade inplace.

The posterior (center) blade may be coupled to the nerve monitoringsystem to conduct nerve monitoring during advancement of the retractorassembly and/or during retraction. According to a first embodiment, theblade may be formed of a conductive material (e.g. aluminum) and coatedwith an insulative coating. A stimulation signal utilized for the nervemonitoring may then be transmitted through the blade and exit into thebody tissue through an uninsulated electrode on the distal end. Aspecial set screw, which connects the retractor blade to the nervemonitoring system may be utilized to prevent current shunting. The setscrew includes a nonconductive lower end which contacts the retractorbody, while the threaded section that contacts the retractor blade isconductive. According to a second embodiment, the blade may beconfigured to receive and couple to a disposable electrode. Thedisposable electrode may be, by way of example, plastic part with aconductive trace deposited along the length of the disposable electrode.An exposed area of the conductive trace at a proximal end of theelectrode couples with the nerve monitoring system. An exposed area atthe distal end of the disposable electrode transmits a stimulationsignal from the nerve monitoring system to the tissue adjacent thedistal end of the retractor blade. The disposable electrode may coupleto engagement features formed in the posterior blade. The disposableelectrode may be situated within a channel formed in the blade. Thedistal end of the posterior blade may include a cut-out that exposes thedistal end of the disposable electrode to tissue posterior to the blade.An intradiscal shim for use with the posterior blade/disposableelectrode combination may preferably be coated with an insulativecoating to prevent current shunting.

BRIEF DESCRIPTION OF THE DRAWINGS

Many advantages of the present invention will be apparent to thoseskilled in the art with a reading of this specification in conjunctionwith the attached drawings, wherein like reference numerals are appliedto like elements and wherein:

FIG. 1 is a FIG. 3 is a top-down view depicting the creation of alateral access corridor formed with a surgical access system via alateral approach through the side of the patient to the target discspace, according to one example embodiment;

FIG. 2 is a perspective view of one example of a tissue retractionassembly forming part of a surgical access system according to oneembodiment of the present invention, shown in a fully retracted or“open” position;

FIG. 3 is a top perspective view of the tissue retraction assembly ofFIG. 2, shown in a fully retracted or “open” position;

FIG. 4 is a top perspective view of the tissue retraction assembly ofFIG. 2 shown in a fully closed position;

FIG. 5 is a perspective view of the tissue retraction assembly of FIG. 2shown in a fully closed position;

FIG. 6 is a top view of the tissue retraction assembly of FIG. 2 shownin a partially open position according to the present invention;

FIG. 7 is a perspective view of the tissue retraction assembly of FIG. 2shown in a partially open position according to the present invention;

FIGS. 8-9 are perspective views of the front side and back side,respectively, of an example of a contoured shim forming part of thesurgical access system of the present invention;

FIG. 10 is an perspective view of the contoured shim of FIG. 8 connectedto a retractor blade;

FIGS. 11-12 are front perspective and back perspective views,respectively, of one example of a locking shim forming part of thesurgical access system of the present invention;

FIG. 13 is a top view of the locking shim of FIG. 11;

FIG. 14 is a perspective view of an example of a shim removal toolaccording to one embodiment of the present invention;

FIG. 15 is a perspective view of the distal portion of the shim removaltool of FIG. 14 engaged with the locking shim of FIG. 11;

FIG. 16 is a perspective view of the distal portion of the shim removaltool of FIG. 14;

FIG. 17 is a perspective view of the distal portion of the shim removaltool of FIG. 15 with the grip extension removed;

FIG. 18 is a top plan view of the arms of the tissue retraction assemblyof FIG. 2;

FIG. 19 is a bottom plan view of the arms of the tissue retractionassembly of FIG. 2;

FIG. 20 is a perspective view of an arm member comprising part of thetissue retraction assembly of FIG. 2;

FIGS. 21-24 are exploded and perspective views of a distal pivot memberand gear member forming part of the arm member of FIG. 20;

FIG. 25 is a rear perspective view of an anterior retractor bladeforming part of the tissue retraction system of FIG. 2;

FIG. 26 is a front perspective view of the anterior retractor blade ofFIG. 25;

FIG. 27 is a top perspective view of the anterior retractor blade ofFIG. 25;

FIG. 28 is a perspective view of the blade assembly portion of thetissue retraction system of FIG. 2 with the anterior retractor blade ofFIG. 25 attached thereto;

FIG. 29 is a front perspective view of the blade assembly portion of thetissue retraction system of FIG. 2 shown in a fully closed position;

FIG. 30 is a top perspective view of the blade assembly portion of FIG.29 shown in a partially open position;

FIG. 31A is a perspective view of a setscrew used to attach theposterior retractor blade to the tissue retraction system of FIG. 2;

FIG. 31B is a side cross section view of the set screw of FIG. 31Acouple to the retractor assembly of FIG. 2;

FIG. 32 is a top perspective view of a posterior translation mechanismforming part of the tissue retraction system FIG. 2, engaged with awrench and attachment arm according to one aspect of the presentinvention;

FIG. 33 is a bottom perspective view of the posterior translationmechanism of FIG. 32;

FIG. 34 is a side perspective view of the posterior translationmechanism of FIG. 32;

FIG. 35 is a perspective view of the wrench of FIG. 32;

FIGS. 36-38 are side views of the attachment arm of FIG. 32;

FIG. 39 is a top perspective view of the tissue retraction assembly ofFIG. 2 engaged with an attachment arm of FIG. 35;

FIGS. 40-41 are side and perspective views, respectively, of an exampleof a disposable electrode forming part of the tissue retraction systemof FIG. 1 according to one embodiment of the present invention;

FIGS. 42-43 are perspective views of an example of a retractor bladeforming part of the tissue retraction system of FIG. 1 configured toreleasably couple with the disposable electrode of FIG. 41;

FIG. 44 is top perspective view of the retractor blade of FIG. 42;

FIGS. 45-46 are perspective views of an assembly comprising thedisposable electrode of FIG. 40 coupled to the retractor blade of FIG.42;

FIGS. 47-48 are perspective views of the tissue retraction assembly ofFIG. 2 including the disposable electrode/blade assembly of FIG. 45;

FIGS. 49-51 illustrate an example of an insulated locking shim for usewith the center blade forming part of the tissue retraction system ofFIG. 2 to prevent current shunting from the center blade whenneurophysiologic monitoring is performed from the center blade;

FIGS. 52-55 illustrate an example of a shim removal tool for use withthe locking shim of FIG. 49;

FIG. 56 illustrates a second example of a shim removal tool for use withthe locking shim of FIG. 49;

FIG. 57 is a perspective view of an example of a nerve monitoring systemprogrammed to perform nerve monitoring before, during and after thecreation of an operative corridor to a surgical target site using thesurgical access system of FIG. 2 in accordance with the presentinvention;

FIG. 58 is a block diagram of the nerve monitoring system shown in FIG.57; and

FIGS. 59-60 are examples of screen displays illustrating exemplaryfeatures and information communicated to a user during the use of thenerve monitoring system of FIG. 57.

DETAILED DESCRIPTION

Illustrative embodiments of the invention are described below. In theinterest of clarity, not all features of an actual implementation aredescribed in this specification. It will of course be appreciated thatin the development of any such actual embodiment, numerousimplementation-specific decisions must be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints, which will vary from one implementation toanother. Moreover, it will be appreciated that such a development effortmight be complex and time-consuming, but would nevertheless be a routineundertaking for those of ordinary skill in the art having the benefit ofthis disclosure. It is furthermore to be readily understood that,although discussed below primarily within the context of spinal surgery,the surgical access system of the present invention may be employed inany number of anatomical settings to provide access to any number ofdifferent surgical target sites throughout the body. It is alsoexpressly noted that, although shown and described herein largely withinthe context of a preferred lateral surgery in the lumbar spine, some orall of the components of the access system described may be employed inany number of other spine surgery access approaches. By way of example,in addition to accessing a lumbar disc space (e.g. for fusion, totaldisc replacement, corpectomy, etc. . . . ), the surgical access systemor some of its components may be used to access the lateral aspect ofthe thoracic spine (e.g. for fusion, total disc replacement, corpectomy,etc. . . . ), and the posterior spine (e.g. for posteriordecompression). By way of further example, it is contemplated that thesurgical access system or some of its components may be used to accessany of the posterior, postero-lateral, anterior, and anterolateralaspects of the spine, and may be employed in the lumbar, thoracic and/orcervical spine.

The instruments and methods described herein are designed and optimizedfor creating a lateral access corridor to the lumbar spine. Accessingthe targeted spinal site through the lateral access corridor avoids anumber of disadvantages associated with posterior access (e.g.

cutting through back musculature and possible need to reduce or cut awaypart of the posterior bony structures like lamina, facets, and spinousprocess) and anterior access (e.g. use of an access surgeon to movevarious organs and blood vessels out of the way in order to reach thetarget site). According to one example, the lateral access approach tothe targeted spinal space may be performed according to the methodsdescribed in U.S. Pat. No. 7,207,949 entitled “Surgical Access Systemand Related Methods,” and/or U.S. Pat. No. 7,905,840 entitled “SurgicalAccess System and Related Methods,” the entire contents of which areeach incorporated herein by reference as if set forth herein in theirentireties.

With reference to FIGS. 1-2, a discussion of the lateral access methodsis provided in brief detail. With the patient 1 positioned on theirside, a surgical access system 6 is advanced through an incision 2, intothe retroperitoneal space 3, and then through the psoas muscle 4 untilthe targeted spinal site (e.g. the disc space 5 between a pair ofadjacent vertebral bodies) is reached. The access system 6 may includeat least one tissue dilator, and preferably includes a sequentialdilation system 7 with an initial dilator 8 and one or more additionaldilators 9 of increasing diameter, and a tissue retractor assembly 10.As will be appreciated, the initial dilator 8 is preferably advanced tothe target site first, and then each of the additional dilators 9 ofincreasing diameter are advanced in turn over the previous dilator. Ak-wire (not shown) may be advanced to the target site and docked inplace (for example, by inserting the k-wire into the vertebral disc)prior to, in concurrence with, or after advancing the initial dilator 8to the target site. With the sequential dilation system 7 positionedadjacent the target site (and optionally docked in place via thek-wire), the retractor assembly 10 is then advanced to the target siteover the sequential dilation system 7.

According to the embodiment shown, the retractor assembly 10 includesretractor blades 12, 16, 18 and a body 20. According to the preferredmethod, the retractor assembly 10 is advanced over the dilation system 7such that the center retractor blade 12 is the posterior most blade. Thesequential dilation system 7 is removed and the retractor assembly 10 isoperated to expand the operative corridor. That is, the retractor blades12, 16, and 18 are separated (FIG. 1), providing the lateral accesscorridor through which instruments and implants may be advanced to thetarget site. It will be appreciated that any number of procedures may beperformed on the spine through the lateral access corridor (e.g. thesurgeon may perform a fusion procedure, a total disc replacement, acorpectomy, etc. . . . ). According to one example, the posterior blade12 may be fixed in position relative to the spine prior to opening theretractor blades. This may be accomplished, for example by attaching ashim to the blade (e.g. via a blade track including dove tail groovesformed on the interior of blade) and inserting the distal end of theshim into the disc space. Alternatively, or in addition, the posteriorblade 12 may be fixed in position by connecting an articulating armbetween the surgical table (or other suitable mount) and the translatingarm associated with the center blade 12). In this manner, the posteriorblade 12 will not move posteriorly (towards nerve tissue located in theposterior portion of the psoas muscle). Instead, the blades 16 and 18will move away from the posterior blade 12 to expand the accesscorridor.

Additionally, nerve monitoring (including determining nerve proximityand optionally directionality) is preferably performed as each componentof the access system 6 is advanced through the psoas muscle, protectingthe delicate nerve tissue running through the psoas, as described in the'949 patent and '668 application. Monitoring the proximity of nerves notonly allows the surgeon to avoid delicate nerves as the access system isadvanced to the spine, but by determining the location of the nervesalso allows the surgeon to position the posterior blade more posterior(e.g. all the way back to the exiting nerve roots), thus exposing agreater portion of the target site than would otherwise be safelyachievable.

With the lateral access corridor formed the target site may be operatedon. For example, when performing a fusion procedure through the lateralaccess corridor, the disc space 5 may prepped for insertion of animplant preparation of the disc space may include performing anannulotomy, removal of disc material, and abrasion of the endplates, andinstruments such as annulotomy knives, pituitaries, curettes, disccutters, endplate scrapers may be used. An implant may be inserted intothe disc space. Fusion promoting materials may be implanted within thedisc space 5 in and around the implant. Fixation may be performedthrough the lateral access corridor, or through different approaches.

The retraction assembly described herein is well suited for creating thelateral access corridor to the lumbar spine as described above. FIGS.2-7 illustrate a tissue retraction assembly 10 forming part of asurgical access system according to the present invention, including aplurality of retractor blades 12, 16, 18 extending from a body 20. Byway of example only, the body 20 is provided with a first retractorblade 12, a second retractor blade 16, and a third retractor blade 18.FIG. 2 illustrates the tissue retraction assembly 10 in a fullyretracted or “open” configuration, with the retractor blades 12, 16, 18positioned a distance from one another so as to form an operativecorridor 15 therebetween which extends to a surgical target site (e.g.an annulus of an intervertebral disc). In one exemplary aspect, theblades 16, 18 are capable of being pivoted or rotated relative to thehandle 20, as best appreciated with combined reference to FIGS. 2 & 3.FIGS. 4-5 show the tissue retraction assembly 10 in an initial “closed”configuration, with the retractor blades 12, 16, 18 generally abuttingone another. FIGS. 6-7 show the tissue retraction assembly 10 in a“partially open” configuration.

The body 20 may be coupled to any number of mechanisms for rigidlyregistering the body 20 in fixed relation to the operative site, such asthrough the use of an articulating arm mounted to the operating table(not shown). The body 20 includes first and second arm members 26, 28hingedly coupled via coupling mechanism shown generally at 30. Thesecond retractor blade 16 is rigidly coupled (generally perpendicularly)to the end of the first arm member 26. The third retractor blade 18 isrigidly coupled (generally perpendicularly) to the end of the second armmember 28. The first retractor blade 12 is rigidly coupled (generallyperpendicularly to) a translating member 17, which is coupled to thebody 20 via a linkage assembly shown generally at 14. The linkageassembly 14 includes a roller member 34 having a pair of manual knobmembers 36 which, when rotated via manual actuation by a user, causesteeth 35 on the roller member 34 to engage within ratchet-like grooves37 in the translating member 17. Thus, manual operation of the knobs 36causes the translating member 17 to move relative to the first andsecond arm members 26, 28.

Through the use of handle extenders 31, 33, the arms 26, 28 may besimultaneously opened such that the second and third retractor blades16, 18 move away from one another. In this fashion, the dimension and/orshape of the operative corridor 15 may be tailored depending upon thedegree to which the translating member 17 is manipulated relative to thearms 26, 28. That is, the operative corridor 15 may be tailored toprovide any number of suitable cross-sectional shapes, including but notlimited to a generally circular cross-section, a generally ellipsoidalcross-section, a generally triangular cross-section, and/or an ovalcross-section. Optional light emitting devices (not shown) may becoupled to one or more of the retractor blades 12, 16, 18 to directlight down the operative corridor 15.

The retractor blades 12, 16, 18 may be composed of any rigid materialsuitable for introduction into or around the human body, including butnot limited to aluminum, titanium, stainless steel, and/or clearpolycarbonate, that would ensure rigidity during tissue distraction. Theretractor blades 12, 16, 18 may be optionally coated with a carbon fiberreinforced coating to increase strength and durability. The retractorblades 12, 16, 18 may be optionally constructed from partially or whollyradiolucent materials (e.g. aluminum, PEEK, carbon-fiber) to improve thevisibility of the surgeon during imaging (e.g. radiographic, MRI, CT,fluoroscope, etc.). Likewise, the retractor body may be composed of anynumber of rigid materials, particularly including, but not limited toaluminum, stainless steel, carbon-fiber, and titanium. According to apreferred embodiment, the retractor blades 12, 16, and 18 and body arecomprised of stainless steel. The stainless steel has a greaterstiffness than other more radiolucent materials (e.g. aluminum) and thuseliminates, or at least reduces, toeing inward (blade flex) of theblades and potential intraoperative breakage. While the stainless steeldoes not have the radiolucent characteristics of other materials oftenused for spinal retractors, the added stiffness (in addition to thedesign of the blade rotation gear 79) permits the body to be constructedwith less material. Thus cutouts through the body and reduced geometryof the body permit fluoroscopic visibility through the retractorassembly 10 where necessary, without sacrificing the strength andstiffness of the retractor. By way of example only, the cutouts 17 a and17 b and indents 17 c of the translating arm 17 allow optimalvisualization of pertinent areas (e.g. posterior border of the vertebralbodies in a lateral fluoroscopy image) without sacrificing stiffness.The retractor blades 12, 16, 18 may be provided in any number ofsuitable lengths, depending upon the anatomical environment and surgicalapproach, such as (for example) the range from 20 mm to 180 mm. Based onthis range of sizes, the tissue retraction assembly 10 of the presentinvention is extremely versatile and may be employed in any of a varietyof desired surgical approaches, including but not limited to lateral,posterior, postero-lateral, anterior, and antero-lateral, by simplyselecting the desired size retractor blades 12, 16, 18 and attachingthem to the body 20 as will be described herein.

The retractor blades 12, 16, 18 may be equipped with various additionalfeatures or components. By way of example only, one, or more of theretractor blades 12, 16, 18 may be equipped with a shim, such as acontoured extender shim 22 or a locking shim 25 as shown in FIGS. 8-13.In a preferred embodiment, the contoured extender shims 22 are suitablefor engagement with the caudal/cephalad retractor blades 16, 18, whilethe interdiscal locking shim 25 is suitable for engagement with thecenter blade 12. However, it should be noted that any shim 22, 25 may beused with any blade 12, 16, 18 without departing from the scope of thepresent invention. Referring to FIGS. 8-10, the contoured extender shim22 extends from retractor blades 16, 18 (as shown on one retractor blade18 in FIG. 10) to form a protective barrier to prevent the ingress oregress of instruments or biological structures (e.g. nerves,vasculature, etc.) into or out of the operative corridor 15. By way ofexample only, the contoured extender shim 22 includes a front, faceconfigured to form a portion of the operative corridor and having agenerally concave surface 300. The contoured extender shim 22 furtherincludes a back surface 302 configured to face the retractor blade 18and having a generally convex shape. The contoured extender shim 22further has a pair of elongated tab members 304 that are configured toslideably engage elongated slot members 306 that run the length of theinside surface of the retractor blade 18. The contoured extender shim 22further includes a deflectable tab 308 near the proximal end of thecontour extender 22. The deflectable tab 308 includes a knob 310extending away from the deflectable tab 308 on the back side of thecontoured extender shim 22. The knob 310 is configured to engage withindentations 312 positioned along the retractor blade 18 to provide fora lock-stop mechanism securing the contoured extender shim 22 inposition during use. In this fashion the contoured extender shim 22 isadvanced distally along the retractor blade 18 until a desired positionhas been reached. The contoured distal end of the contoured extendershim 22 is shaped to conform to the vertebral body to maximize contactwith the vertebral body, particularly near the anterior drop, andprevent tissue creep into the exposure. For example, the distal end mayhave a curved surface such that one longitudinal edge of the contouredextender shim 22 is longer than the other longitudinal edge. Forexample, the geometry of the distal end 23 allows it to contour to theanterior drop off of the vertebral body as the retractor is openedanteriorly.

Referring to FIGS. 11-13, the locking interdiscal shim 25 has a distaltapered region 45 which may be advanced into the disc space for thepurpose of distracting the adjacent vertebral bodies (thereby restoringdisc height) and/or anchoring the blade 12 relative to the spine. Insimilar fashion to the contoured extender shim 22, the lockinginterdiscal shim 25 also forms a protective barrier to prevent theingress or egress of instruments or biological structures (e.g. nerves,vasculature, etc.) into or out of the operative corridor 15. The lockinginterdiscal shim 25 locks in position on the retractor blade 12 toprevent the shim from dislodging and allowing the retractor to move fromthe targeted location. To lock position on the blade, the shim 25 has aflexible engagement tab 320 with a ramped leading edge 49 that allows itto advance down indentations 312 on the inner surface of the retractorblade 12. The trailing edge 27 of the engagement tab 320 is squared toprevent disengagement (thus preventing unwanted backout of the shim)from the indentation 312 without use of a removal tool 43. Theengagement tab 320 also includes a T-shaped removal lip 55 configured toengage a shim removal tool, as described below. The T-shaped lip 55 ofthe engagement tab 320 allows the removal tool 43 to lift the square lip27 away from the retractor blade 12 and remove the shim 25. The lockinginterdiscal shim 25 has a pair of elongated tab members 322 that areconfigured to slideably engage elongated slot members 306 that run thelength of the inside surface of the retractor blade 12. The lockinginterdiscal shim 25 includes a dimple or aperture 56 located near theproximal end of the shim 25 configured for engagement with a shimremoval tool, as will be explained in further detail below.

FIGS. 14-17 illustrate an example of a shim removal tool 43 forextracting the locking interdiscal shim 25 from a retractor blade 12,which in the example provided resembles a Kerrison-style removal tool.By way of example only, removal tool 43 is shown and described herein inconjunction with locking interdiscal shim 25, although it is to bereadily appreciated that removal tool 43 may be employed in a similarmanner with other locking shims without departing from the scope of thepresent invention. The removal tool 43 includes a squeezable handle 46,an elongated region 47 including a stationary arm 330 and a translatingarm 332, and a distal end 48. The squeezable handle 46 includes a fronthandle 46 a and back handle 46 b. The front handle 46 a is pivotablyconnected to the translating arm 332, while the back handle 46 b isimmovably connected to the stationary arm 330. The distal end 48includes a grip extension 334 configured to interact with both theretractor blade 12 and the interdiscal locking shim 25. The gripextension 334 includes a track guide 336 that slideably engages theelongated slot members 306 as described above in relation the shims 22,25. The distal end of the grip extension 334 includes a pair of arms 338extending distally from the grip extension 334 in a generally parallelfashion. The arms 338 include a ramped surface 340 sloped such that thethickness of the arms 338 at their distal ends is considerably less thanthe thickness of the arms 338 at their proximal ends where they extendfrom the grip extension 334. The ramped surface 340 may be planar orhave a concave curvature without departing from the scope of the presentinvention. The distal end of the translating arm 332 includes atranslating plate 342. The translating plate is generally planar and,includes a dimple or recess 344 positioned on the lower surface 346 ofthe translation plate 342. The recess 344 is configured to receive alocking ball 348 when the removal tool 43 is in a neutral position (i.e.when the handles 46 a, 46 b are released).

To use the removal tool 43, the distal end 43 including the gripextension 334 is slideably advanced along the retractor blade 12 withthe handle 46 in the neutral position until the ramped arms 338 engagethe removal lip 55 of the shim 25. When the handle 46 is in the neutralposition, the locking ball 348 retreats into the recess 344 of thetranslating plate 342 allowing the distal end 48 of the grip extension334 to engage flush with the shim 25. When the ramped arms 338 engagethe removal lip 55 of the interdiscal locking shim 25, the lip 55 isdeflected outward lifting the engagement tab 320 away from the retractorblade 12. Simultaneously, the locking ball becomes positioned in theaperture 56 of the locking shim 25. Squeezing the front handle 46 acauses the translating arm 332 to slideably translate forward relativeto the stationary arm 330. This translates the position of the recess344 on the translating plate 342 such that the locking ball 348 isprevented from entering the recess 344. With the locking ball positionedwithin aperture 56, the removal tool 43 is now locked to the lockingshim 25 such that the shim 25 may be removed by applying a force in aproximal direction relative to the retractor blade 12. Thus, squeezingthe removal tool handle 46 locks the distal end 48 to the interdiscallocking shim 25 while disengaging the the lip 55 of the engagement tab320 from the indentation 312 of the retractor blade 12, enabling theuser to pull up and remove the shim.

Shim elements 22, 25 may be made from any rigid material suitable foruse in the human body, including but not limited to biologicallycompatible plastic and/or metal (such as aluminum, PEEK, carbon-fibersand titanium). According to one example, the extender shims 22 may bemade from plastic and the interdiscal shim 25 may be made of metal. Theinterdiscal shim 25 may also be coated with an insulative coating (e.g.a parylene coating) to prevent current shunting or density changes fromelectrodes situated at the distal end of the retractor blade 12.Retractor extender shim 22 may have symmetric narrow configurations(FIGS. 8-9), which do not extend laterally from the retractor blade,and/or broad configurations (not shown) that extend laterally from eachside of the retractor blade, and/or an asymmetric configuration (notshown) which extends laterally from one side of the retractor blade. Theshim elements 22, 25 may be composed of a material that would destructwhen autoclaved (such as polymer containing a portion of glassparticles), which may be advantageous in preventing the unauthorizedre-use of the retractor extender shim 22 and/or the shim element 25(which would be provided to the user in a sterile state).

Referring now to FIGS. 18-24, the mechanisms associated with the armmembers 26, 28 will be discussed in further detail. Although theinventive features will be discussed in relation to the first arm member26 only, it should be understood that the second arm member 28 isvirtually a mirror image of the first arm member 26 such that featuresshown and described with respect to the first arm member 26 may bepresent with respect to the second arm member 28 without departing fromthe scope of the present invention. Referring first to FIGS. 18-19, thedistal region of the body 20 is shown in greater detail. Each arm member26, 28 includes a distal pivot member 70 and a proximal arm portion 71.Referring also to FIG. 20, which shows the first arm member 26 ingreater detail, the distal pivot member 70 extends distally from theproximal arm portion 71 and includes portions of the rotating gearmechanism 79 (described in detail below) housed within the proximal armportion 71. This position of the gear mechanism proximal to theretractor blades and operative corridor allows the blades to be splayedwithout inhibiting visualization of the corridor during adjustment. Theproximal arm portion 71 includes a coupling aperture 72 through whichthe coupling element 30 passes, a proximal attachment region 74 at whichhandle extender 31 may be attached, an aperture 76 through which knob 36passes, and a gear aperture 352 configured to allow passage of the uppercap 364 and post head 374 of the gear mechanism 79 to allow foraccessibility of post head 374 to impart rotation of the retractorblades. The body 20 further includes a restrictor element 97 formed byportions of the distal pivot member 70 and the proximal portion 71working in concert to restrict the degree of allowable angulation forthe retractor blades. At the distal end of the distal pivot member 70 isa blade aperture 78 and a screw aperture 80. The blade aperture 78 isconfigured to receive an attachment post of the retractor blade 16, 18to couple the blade to the body 20. The screw aperture 80 threadablyreceives a setscrew 350 for reversibly securing the retractor blade 16,18 to the body 20. Translating member 17 is shown by way of example onlyas having a large viewing aperture 17 a which functions to increasevisibility during fluoroscopy.

FIGS. 21-24 illustrate and example of the gear mechanism 79 of thedistal pivot member 70 in greater detail. The gear mechanism generallycomprises a lead screw driven rack and pinion gear including atranslating rack (translating gear 360) and a section gear rotatingpinion (rotating gear 368). By way of specific example, the gearmechanism 79 includes a translating gear 360, a lead screw 362, an uppercap 364, a lower cap 366 and a rotation gear 368. The translating gear360 includes a central threaded aperture 370 extending therethrough andgear teeth 372 oriented generally horizontally on the outside surface.The lead screw 362 includes post head 374, a threaded region 376, acircumferential ridge 378 positioned between the post head 374 and thethreaded region 376, and a non-threaded foot 380. The post head 374 maybe configured in any shape desirable to engage a rotation tool to effectrotation of the lead screw, including but not limited to the hexagonalshape shown by way of example only in FIG. 21. The threaded region 376is configured to engage with the threaded aperture 370 of thetranslating gear 360. As will be described in detail below, duringoperation the translating gear 360 translates linearly along thethreaded region 376 of the lead screw 362. The upper cap 364 has agenerally circular cross-section and includes a central open aperture382 configured to receive the post head 374 therethrough andcircumferential threads 384 configured to threadedly secure the uppercap 354 to the arm member 26. The lower cap 366 includes a centralclosed aperture 386 configured to receive the foot 380 of the lead screw362 therein and circumferential threads 388 configured to threadedlysecure the lower cap 366 to the first arm member 26. The rotation gear368 includes at least one horizontal gear tooth 390 extending laterallytherefrom and a connector post 392 extending distally therefrom. Thehorizontal gear tooth 390 engages with the gear teeth 372 of thetranslating gear 360. The connector post 392 is received within anaperture 394 within the distal pivot member 70. A pin 396 is furtherprovided to secure the connector post 392 to the distal pivot member 70.

In use, a user engages a rotation tool to the post head 374 and rotatesin a clockwise direction. This causes the lead screw 362 to rotate.According to one example, the rotation tool may include a torquelimiting feature to prevent loading of the retractor blades should theybecome stuck on bone (e.g. osteophytes) or features. The lead screw 374bottoms out in the closed aperture 386 of the lower cap 366. The ridge378 engages with the lower surface of the upper cap 364 ensuring thatthe lead screw 374 is only able to rotate without any translationalmovement. Due to the threaded engagement with the translating gear 360,rotation of the lead screw 362 causes the translating gear 360 totranslate linearly along the lead screw. Interaction between the gearteeth 372 of the translating gear 360 and the gear teeth 390 of therotating gear 368 cause the rotating gear 368 to rotate. Because therotation gear 368 is securely fastened to the distal pivot member 70 viathe interface between the connector post 392 and aperture 394, thisaction in turn causes the distal pivot member 70 to pivot. FIG. 24illustrates the directional movement of the various parts.

The distal pivot member 70 includes an extension 398 in which theaperture 394 is located, and a recess 400 extending partially around theoutside edge of the distal pivot member 70. The recess 400 forms part ofthe restrictor element 97 and is wider than the corresponding extensionon the arm 26 that it receives therein. When the distal pivot member 70rotates, contact between the extension and the wall of the recess 400prevents further movement. Thus, the size of the recess 400 and/orextension can be set such that blade splay or rotation is containedwithin a desired range. By way of example only, this range may bebetween 0 and 20 degrees. However, a larger range of angulation may bepossible without departing from the scope of the invention, for examplerange of 0-30 degrees and 0-45 degrees are also contemplated.

Initially, the retractor assembly 10 of the present invention isintroduced to the surgical target site with the retractor blades 12, 16,18 in a first, fully closed position (shown generally in FIGS. 4-5). Inthis configuration, the retractor blades 16, 18 are oriented in agenerally perpendicular configuration. In some instances it may bedesirable to pivot either the second retractor blade 16 or the thirdretractor blade 18 (or both) outward in order to increase the volume ofthe operative corridor 15 (by increasing the distal dimension of theoperative corridor). To accomplish this (with respect to blade 16), afemale hexagonal driver is engaged to the post head 374 of first arm 26.When the post head 374 is rotated in a clockwise direction, the blade 16will pivot in a lateral (outward) direction. When rotating the post head374 in a counter-clockwise direction, the blade 16 will pivot a lateral(inward) direction. The blade splay mechanism 79 employed provides forcontinuous splay (i.e. may be splayed to any angulation from 0 degreesto a maximum permissible angulation). According to the preferredexample, a restrictor element 97 prevents angulation above a maximumpermissible angle. For example, the maximum permissible angle may be 20degrees. The restrictor element may also permit the blade from splayinginward past 0 degrees.

The blade 18 may be pivoted independently of blade 16 such thatdifferent angles for each blade 16, 18 are achieved. Thus, it may bedesirable to use blades of differing lengths and still maintain asymmetrical operating corridor wherein the distal ends of blades 16, 18are oriented along the same general plane. Before removing the tissueretraction system 10 from the operative corridor, the post head 374should be rotated in a counter-clockwise direction, allowing theretractor blade 16 to return to their initial alignment (i.e., generallyperpendicular to the handle 20) to facilitate removal. It will beappreciated that the direction of rotation could be reversed by simplyreversing the thread direction on the actuating screw and translationgear. Furthermore, although the upper cap 364 and lower cap 366 havebeen described as being secured to the arm 26 via a threaded engagement,any type of engagement is possible, including but not limited towelding, press-fit, and the like.

Referring to FIGS. 25-28, a supplemental anterior retractor blade 60 maybe provided for optional use with the tissue retraction assembly 10described herein. Supplemental anterior retractor blade 60 provides forselectively increasing the number of retractor blades forming theoperative corridor during (or before) use. The ability to selectivelyincrease the number of retractor blades affords additional user controlover the size and/or configuration of the access corridor,advantageously increasing the versatility of retractor assembly 10.Although supplemental anterior retractor blade 60 is shown and describedherein in use with a three-bladed configuration of the retractorassembly 10 (thereby comprising a fourth retractor blade as referencedherein), it is to be readily appreciated that the supplemental anteriorretractor blade 60 may be used with a retractor assembly 10 configuredwith any number of primary retractor blades.

As illustrated in FIGS. 25-28, supplemental anterior retractor blade 60comprises a handle 61, a connecting device 62, a grooved area 64, and ablade 63. The supplemental anterior retractor blade 60 is connected toretractor blades 16, 18. The connecting device 62 slidably interlockswith the holding knobs 19 (FIGS. 29-30), and the retractor blades 16, 18can move freely (i.e., “open” and “close”) while the connecting device62 remains interlocked with the holding knobs 19. The wider end of the,holding knobs 19 prevent the connecting device 62 from becomingdisconnected. The grooved area 64 of the anterior retractor blade 60interlocks with the connecting device at the desired depth. The anteriorretractor blade may be made from any rigid material suitable for use inthe human body, including but not limited to biologically compatibleplastic and/or metal (such as aluminum, PEEK, carbon-fibers, stainlesssteel, and titanium). The anterior retractor blade 60 may be provided inany number of suitable lengths, depending upon the anatomicalenvironment, surgical approach, and length of primary retractor blades12, 16, 18, such as (by way of example only) the range from 20 mm to 180mm.

With reference to FIG. 2, a preferred method of using supplemental bladeassembly 60 in conjunction with retractor assembly 10 is shown. Theretractor assembly 10 is first advanced to the target site (after tissuedistraction) and an initial operating corridor is formed according tothe methods described above (i.e. moving retractor blades 16, 18 from a“closed” position to a “retracted” position). Once the operatingcorridor is created with primary retractor blades 12, 16, 18, thesupplemental anterior retractor blade 60 may be utilized to expand theoperating corridor and/or provide an extra barrier to prevent ingress ofbody tissue into the corridor. To do so, the connecting device 62 isslidably secured onto the holding knobs 19, and the grooved area 64 theninterlocks with the connecting device. This, along with the pressure ofthe tissue, holds the anterior retractor blade in position. Preferably,when retracting the tissue, the connecting device 62 is used as afulcrum and the handle 61 is pulled like a lever inward (i.e., towardsthe retractor assembly 10) and the distal end of the blade will pivot atan outward angle along the x-axis.

FIGS. 32-35 illustrate an example of a contemplated alternativeembodiment to the translating arm 17 which could be replace thetranslating arm 17 on the retractor assembly 10. The alternativetranslating arm 91 forms a posterior translation mechanism 90,illustrated in FIGS. 32-35. The posterior translation mechanism 90permits controlled posterior translation when desired, without thecompromising the position of the retractor body in other directions(i.e., caudal-cephalad alignment). By way of example only, the posteriortranslation mechanism 90 allows for the surgeon to change the positionof the blade assembly 21 inside of the surgical site without changingthe size of the incision. The wrench 93 secures onto the hexagonallocknut 92 at the distal end, which is a female hexagonal shape 94.Turning the wrench handle 95 clockwise loosens the hexagonal locknut 92,which loosens the connection between the center translating arm 91 andthe articulating arm attachment 96. This allows the retractor assembly10 to be posteriorly translated up to a maximum length of the posteriortranslation slot (e.g. up to 10 mm in this example) with respect to thearticulating arm attachment 96 by pulling the retractor assembly 10posteriorly. The hexagonal locknut 92 must be fastened after posteriortranslation. Thus, if a surgeon loses alignment during surgery, he orshe can realign the retractor assembly 10 posteriorly with ease andsafety.

FIGS. 36-39 illustrate an example of an articulating arm attachment 100according to one embodiment of the present invention. The articulatingarm attachment 100 includes a quick align feature for preliminaryengagement of a toothed connector. This feature provides the physicianwith the means to properly and securely align the teeth (i.e., peaks andvalleys) of the connector for intersection single handledly. Thisfeature avoids locking the connectors together before their teeth areproperly aligned. This can happen when the teeth become worn and it ismore difficult to align the peeks of one connector in the valleys of theother connector.

The quick align articulating arm attachment 100 comprises a superiortoothed connector 101, an inferior toothed connector 102, a post 103,and a canted coil ring 104. The canted coil ring 104 rests snugly insidea groove formed in the inferior connector 102. The post 103 screws intoand locks onto the inside of the superior connector 101. The post 103contains a thicker distal end. When connecting toothed connectors 101,102, the distal end of the post 103 pushes through the canted coil ring104, which expands to allow the distal end of the post 103 to passthrough, and then contracts where the post 103 tapers into a groove 107(FIG. 38). When the post 103 is pushed through the canted coil ring 104,and the coil contracts, the connectors 101, 102 are semi-secured inplace. The post 103 is of the proper length that it will only besemi-secured in place when the teeth of the connectors are properlyaligned. The connectors 101, 102 can be disconnected (i.e., pull thepost 103 out of the canted coil ring 104) with a moderate effort. By wayof example only, to connect the arm attachment 96, the knob 106, whichconnects to an elongated screw 105, secures the arm attachment to theassembly by screwing the screw 105 into the inferior connector 102,which contains grooves that the screw 105 secures into. While shown foruse with an articulating arm and the toothed connector assembly of theretractor assembly 10, the quick align connector 100 is suitable for usewith any toothed connector assembly.

As mentioned above, nerve monitoring may be utilized during advancementand retraction of the retraction assembly 10. According to one example,as pictured in FIG. 29, the nerve monitoring component of the retractorsystem is the center retractor blade 12, which may be made of aconductive material (e.g. aluminum) and coated with a insulative coatingto direct stimulation from the nerve monitoring system to the tissueadjacent the distal end. To direct stimulation to the posterior blade12, a stimulation clip 550 of the nerve monitoring system may beconnected to the set screw 13 used to couple the posterior blade 12 tothe translating arm 17. When a stimulation signal is emitted from thestimulation clip 550 it will travel through the set screw 13 and intothe blade through an uninsulated contact region with the blade. In orderto reduce shunting of current between the set screw and retractor body20 a special set screw 760 which is configured to reduce shunting ofelectrical current through the retractor body, as illustrated in FIGS.31A and 31B. The setscrew 760 has a composite (e.g. PEEK) contactsurface 762 where the setscrew 760 engages the retractor body, and ametal contact surface 764 where the setscrew 760 engages the stimulationclip 550. This isolates the electrical current delivered to the centerblade 12 through a stimulation clip 550 to the retractor blade 12 andprevents shunting of the current through the retractor body. Asdescribed above, the blade is generally insulated based on the anodizedaluminum construction. The retractor body which has a DSC coating is notinsulated. Thus the center blade 12 itself insulates the current fromthe retractor body at all points of contact except the setscrew 760. Thepeek component 762 at the bottom of the setscrew 760 accomplishes this.

According to another example embodiment, pictured in FIGS. 40-48 thenerve monitoring components of the tissue retraction assembly includes 2main components: a disposable electrode 450 and a center (posterior)blade 500, that replaces the center blade 12, designed to couple to thedisposable electrode 450. A stimulation clip 550 may be used to connectthe disposable electrode to the nerve monitoring system. One potentialadvantage of the disposable electrode and accompanying center blade isthe increased ability to attain consistent and repeatable nervemonitoring functionality throughout the course of a single surgery andfrom surgery to surgery (since there is no risk of erosion of theinsulative coating on the blade which can lead to current shunting). Twopotential barriers to achieving this consistent and repeatablefunctionality are current shunting and reductions in current density atthe distal end of an electrode which can potentially affect thesensitivity of nerve monitoring equipment as a result of conductivemetallic devices in the immediate vicinity of the distal tip of thestimulating electrodes. To combat this potential, a locking intradiscalshim (similar to the shims in FIGS. 11-13) with an insulative coatinghas been developed as a novel solution. By way of the example theinsulative coating may be a parylene coating.

FIGS. 40-48 illustrate an example of one embodiment of the removablycouplable disposable electrode 450 and retractor blade 500 for use withthe tissue retraction assembly 10 according to the present invention.The disposable electrode 450 assists in the detection of nerves duringinsertion and positioning of the tissue retraction assembly within theoperative corridor and surgical target site, as described above (similarto the electrodes 23). Using a disposable electrode permits theretractor blade 500 to be sterilized and reused endlessly without thepossibility of degradation to the electrode. This in turn ensures thatresults from nerve monitoring using the electrode are consistent andreduces potentially high costs of replacing the entire blade structureif the electrode (or insulating regions surrounding the electrode)degrade.

FIGS. 40-41 illustrate one example of a disposable electrode 450 thatincludes a molded plastic part with a conductive trace 451 depositedgenerally along the length of the disposable electrode 450. Preferably,the disposable electrode 450 is made out of a generally stiff materialthat can also withstand bending without breaking, such as, for example,PVC. The conductive trace 451 provides a conductive pathway for thedelivery of current from a current delivery source (such as astimulation clip 550) to the distal end of the disposable electrode 450.There are generally two areas along the disposable electrode where theconductive trace 451 is exposed for enabling the delivery of current toand from the disposable electrode 450. By way of example, the proximalend of the disposable electrode 450 has a first exposed area 452 whichallows a current delivery source to deliver an electric current to theconductive trace 451. The first exposed area 452 may wrap around thecircumference of the proximal end of the disposable electrode 450 toensure a conductive path between the disposable electrode 450 and acurrent delivery device (such as, for example, a stimulation clip 550).The distal end of the disposable electrode 450 has a second exposed area453 (shown by way of example as a triangular patch) for emission of theelectric current from the distal end of the disposable electrode 450.Other than the exposed areas 452, 453, the remainder of the conductivetrace 451 is insulated with a dielectric coating to prevent currentshunting. Any number of conductive materials suitable for completing thecurrent pathway, such as, for example, silver, or copper may be used inthe conductive trace 451 without departing from the scope of the presentinvention.

The first exposed area 452 of the disposable electrode may have agenerally cylindrical shape for facilitating the connection between theelectrode and a nerve monitoring system. For example, as shown in FIGS.47-48, an electrical coupler is shown in the form of a plunger clip.Although shown as cylindrical, the connection site for a currentdelivery device may be any size and shape necessary for making a qualityelectrical connection without departing from the scope of the presentinvention. The remainder of the body of the disposable electrode 450 maybe generally flat with minimal thickness and a variety of features forengaging and securing the disposable electrode 450 to a retractor blade500. For example, wings 455 may extend from the sides of the disposableelectrode 450 for engaging positioning features within the retractorblade 500, as will be discussed in more detail below. Additionally, thedistal end of the disposable electrode 450 may have a ledge 456 forengaging a feature of the retractor blade 500 for further securepositioning of the disposable electrode 450 relative to the retractorblade 500, as will also be discussed in more detail below. A singlesized disposable electrode 450 is designed to be used with a variety ofretractor blade 500 sizes and shapes (for example, retractor bladelengths generally ranging from 20 to 180 mm), but the disposableelectrodes may also be available in a variety of shapes and sizes.

FIGS. 45-46 illustrate one example assembly of a disposable electrode450 releasably coupled to retractor blade 500. Preferably, at least theposterior blade is configured to enable the coupling of a disposableelectrode 450. During assembly of the disposable electrode 450 to theretractor blade 500, the proximal end of the disposable electrode 450(more specifically, adjacent the first exposed area 452 end of thedisposable electrode 450) is inserted into generally the distal end ofthe retractor blade 500. The wings 455 of the disposable electrode 450mate with and are constrained by the dovetail grooves 502 which extendlongitudinally from the distal end to the proximal end of the retractorblade 500. The dovetail grooves 502 provide an insertion guide for thedisposable electrode 450 as it is inserted and assists in maintainingproper positioning of the disposable electrode 450 while coupled to theretractor blade 500. Additionally, the ledge 456 near the distal end ofthe disposable electrode 450 may engage the cut-out 506 generally nearthe distal end of the retractor blade 500 to further assist in securingthe positioning of the disposable electrode 450 relative to theretractor blade 500. Therefore, the disposable electrode 450 is adaptedto the retractor blade 500 so that the second exposed area 453 (shown byway of example as triangular in FIGS. 41 and 45) is exposed generallyalong the outer surface of the blade (best shown in FIG. 45).Furthermore, the proximal end of the disposable electrode 450 protrudesfrom a machined cavity 504 (best shown in FIG. 44) at the proximal endof the retractor blade 500. Depending on the height of the blade, theproximal end may be bent or folded so as not to obstruct the surgicalcorridor. While the disposable electrode 450 and associated retractorblade 500 have been described herein for use with the retractor assembly10, particularly for lateral access to the lumbar spine, it iscontemplated that the disposable electrode retractor blade combinationmay be useful in a variety of surgical procedures (e.g. in a cervicalprocedure for stimulating the recurrent laryngeal nerve to monitorstatus of the nerve during retraction to access the anterior cervicalspine). The cut-out 506 may also be useful as an alignment tool toensure that the retractor assembly is properly aligned. By way ofexample, it is generally preferable to have the posterior blade alignedperpendicular to the disc space such that the cephalad and caudal bladesexpand directly anterior. Holes (not show) may be provided at the distalend of each of the cephalad and caudal blades. The holes will bedistinguishable when viewed on a fluoroscopy image if they are notobstructed by a radiodense object. When the retractor assembly isproperly aligned with the disc space and the retractor blades are in theclosed position, the cut-out 506 is visible in a lateral fluoroscopicimage and the holes line up with the cut-out 506 and are also visible.If the holes are not visible, the retractor may need to be realigned.According to another example, a second set of alignment holes may beincluded (either above or below the first set of holes) such that thehorizontal alignment of the retractor assembly 10 relative to the spinemay also be assessed.

FIG. 49 is illustrates a locking intradiscal shim 600 designed for usewith the center blade 500 and disposable electrode 450, according to anexample embodiment. The locking intradiscal shim 600 is similar to theshim 25 of FIGS. 10-12 such that a description of all the like elementswill not be repeated here. The locking intradiscal shim 600 of FIG. 49is preferably coated with an insulative parylene coating to mitigatecurrent shunting and changes to current density at the distal tip of thedisposable electrode. Parylene is the trade name for a variety ofchemical vapor deposited poly (p-xylylene) polymers used as moisturebarriers and electrical insulators. Among such polymers, Parylene C ismay be particularly suited due to its combination of barrier propertiesand manufacturing advantages. The locking intradiscal shim 600 includesa deflectable tab 602 with a lip member 604 that serves as a lockingfeature. The shim 600 further includes a cut-out 606 that receives anengagement tab of a removal tool. FIGS. 50-51 illustrate the lockingintradiscal shim of FIG. 49 coupled to and extending from the distal endof the blade 500 with the disposable electrode 450 also coupled to theblade 500.

FIGS. 52-55 illustrate a shim removal tool 700 according to a secondexample embodiment. By way of example only, the shim removal tool 700 isshown and described herein in conjunction with the locking intradiscalshim 600 of FIGS. 49 and 50, although it is to be readily appreciatedthat the shim removal tool may be employed in a similar manner withother locking shims according to the present invention.

The shim removable tool 700 includes a proximal grip cage 702, a distalengagement region 704, and an elongated shaft 706 extendingtherebetween. The proximal grip cage may be generally rectangular inshape and provides a grip for manipulating the tool and also provides astrike surface for impacting the instrument if necessary. The grip cage702 also surrounds the thumb release 708, which is connected to thedistal region 704 via a spring mechanism 710. The distal region 704includes a shim fork 712 and a release fork 714. The shim fork 712includes a guide track 716 that engages the track in the retractor blade(described above). The split ramp 718 at the distal end of the shim fork712 slides along the front of the shim 600 and engages behind the lipmember 604, lifting the engagement tab on the back side of the removallip 604 and disengaging the tab from the track guide. This can be doneto remove the shim 600 completely from the blade or to simply repositionthe shim higher (or lower) along the length of the blade track. As thesplit ramp 718 fully seats around the removal lip 604, an engagement tab720 on the shim fork 712 catches in the cutout 606 in the shim 600,locking the shim fork 712 to the shim 600. The release fork 714 may beengaged to remove the engagement tab 720 of the shim fork 712 from theshim 600. Depressing the thumb release 708 moves the release fork 714distally where the split ramp 718 of the release fork 714 engages behindthe removal lip 722 of the shim fork 712, lifting the engagement tab 720out of the cutout 606 in the shim 600. At the same time, knobs 724 onthe release fork 714 push distally on the shim 600 causing the shim fork712 to slide proximally and disengage from the removal lip 604 of theshim 600.

FIG. 56 illustrates a shim removal tool 750 according to a third exampleembodiment. The shim removal tool 750 works like the shim removal tool700 of FIG. 52 except that it includes only a shim fork 752 and not arelease fork. Thus once the shim fork 752 is engaged the shim must beremoved from the blade track before the tool can be disengaged. The shimfork 750 works as described with regard to the removal tool 700. Theremoval tool 750 includes a strike plate 754 for delivering an impactionforce to the removal tool. The strike plate 754 includes a threaded holefor connecting additional instruments such as a slap hammer (to aidremoval of the shim).

As mentioned above, the dilation assembly 7 and retraction assembly 10of the surgical access system 6 may be configured to detect the presenceof (and optionally the distance and/or direction to) neural structuresduring tissue dilation and/or retraction. This is accomplished byemploying the following steps: (1) one or more stimulation electrodesare provided on the various dilation and/or retraction components; (2) astimulation source (e.g. voltage or current) is coupled to thestimulation electrodes; (3) a stimulation signal is emitted from thestimulation electrodes as the various components are advanced towards ormaintained at or near the surgical target site; and (4) the patient ismonitored to determine if the stimulation signal causes musclesassociated with nerves or neural structures within the tissue toinnervate. If the nerves innervate, this may indicate that neuralstructures may be in close proximity to the distraction and/orretraction components.

Neural monitoring may be accomplished via any number of suitablefashions, including but not limited to observing visual twitches inmuscle groups associated with the neural structures likely to found inthe tissue, as well as any number of monitoring systems, including butnot limited to any commercially available “traditional” electromyography(EMG) system (that is, typically operated by a neurophysiologist). Suchmonitoring may also be carried out via the surgeon-driven EMG monitoringsystem shown and described in the '949 and '840 patents referencedabove, as well as PCT Applications PCT/US02/30617 and PCT/US2008/004427,both of which are incorporated herein by reference as if set forthentirely herein. In any case (visual monitoring, traditional EMG and/orsurgeon-driven EMG monitoring), the access system of the presentinvention may advantageously be used to traverse tissue that wouldordinarily be deemed unsafe or undesirable, thereby broadening thenumber of manners in which a given surgical target site may be accessed.

FIGS. 57-58 illustrate one such monitoring system 170, by way of exampleonly, suitable for use with the surgical access system 6 of the presentinvention. The monitoring system 170 includes a control unit 172, apatient module, 174, and an EMG harness 176 and return electrode 178coupled to the patient module 174, and a cable 182 for establishingelectrical communication between the patient module 174 and any numberof surgical accessories 196, including the surgical access system of thepresent invention (retractor assembly 10 of FIG. 2, dilators 8 and 9 ofFIG. 1, K-wire 42 of FIG. 57). The surgical accessories 196 may furtherinclude, but are not necessarily limited to, devices for performingpedicle screw tests (such as a screw test probe 198), neural pathologymonitoring devices (such as a nerve root retractor 200), couplingdevices for electronically coupling surgical instruments to the system170 (such as electric coupling devices 202, 204 and stimulator driver206), and pilot hole forming components (such as a tap member 208,pedicle access probe 210, or other similar device). More specifically,this electrical communication can be achieved by providing, by way ofexample only, a hand-held stimulation driver 206 capable of selectivelyproviding a stimulation signal (due to the operation of manuallyoperated buttons on the hand-held stimulation controller 206) to one ormore connectors (e.g., coupling devices 202, 204). The coupling devices202, 204 are suitable to establish electrical communication between thehand-held stimulation controller 206 and (by way of example only) thestimulation electrodes on the K-wire 42, the dilators 8 and 9, theretractor blades 12, 16, 18, and/or the shim members 22, 25(collectively “surgical access instruments”).

In order to use the monitoring system 170, then, these surgical accessinstruments must be connected to at least one of coupling devices 202,204 (or their equivalent), at which point the user may selectivelyinitiate a stimulation signal (preferably, a current signal) from thecontrol unit 172 to a particular surgical access instruments.Stimulating the electrode(s) on these surgical access instrumentsbefore, during, and/or after establishing operative corridor will causenerves that come into close or relative proximity to the surgical accessinstruments to depolarize, producing a response in a myotome associatedwith the innervated nerve.

The control unit 172 includes a touch screen display 190 and a base 192,which collectively contain the essential processing capabilities(software and/or hardware) for controlling the monitoring system 170.The control unit 172 may include an audio unit 168 that emits soundsaccording to a location of a surgical element with respect to a nerve.The patient module 174 is connected to the control unit 172 via a datacable 194, which establishes the electrical connections andcommunications (digital and/or analog) between the control unit 172 andpatient module 174. The main functions of the control unit 172 includereceiving user commands via the touch screen display 190, activatingstimulation electrodes on the surgical access instruments, processingsignal data according to defined algorithms, displaying receivedparameters and processed data, and monitoring system status and reportfault conditions. The touch screen display 190 is preferably equippedwith a graphical user interface (GUI) capable of communicatinginformation to the user and receiving instructions from the user. Thedisplay 190 and/or base 192 may contain patient module interfacecircuitry (hardware and/or software) that commands the stimulationsources, receives digitized signals and other information from thepatient module 174, processes the EMG responses to extractcharacteristic information for each muscle group, and displays theprocessed data to the operator via the display 190.

In one embodiment, the monitoring system 170 is capable of determiningnerve direction relative to one or more of the K-wire 42, the dilators 8and 9, the retractor blades 12, 16, 18, and/or the shim elements 22, 25before, during and/or following the creation of an operative corridor toa surgical target site. Monitoring system 170 accomplishes this byhaving the control unit 172 and patient module 174 cooperate to sendelectrical stimulation signals to one or more of the stimulationelectrodes, provided on these instruments. Depending upon the locationof the surgical access system 10 within a patient (and moreparticularly, to any neural structures), the stimulation signals maycause nerves adjacent to or in the general proximity of the surgicalaccess system 10 to depolarize. This causes muscle groups to innervateand generate EMG responses, which can be sensed via the EMG harness 176.The nerve direction feature of the system 170 is based on assessing theevoked response of the various muscle myotomes monitored by the system170 via the EMG harness 176.

By monitoring the myotomes associated with the nerves (via the EMGharness 176 and recording electrode 177) and assessing the resulting EMGresponses (via the control unit 172), the surgical access system 10 iscapable of detecting the presence of (and optionally the distant and/ordirection to) such nerves. This provides the ability to activelynegotiate around or past such nerves to safely and reproducibly form theoperative corridor to a particular surgical target site, as well asmonitor to ensure that no neural structures migrate into contact withthe surgical access system 6 after the operative corridor has beenestablished. In spinal surgery, for example, this is particularlyadvantageous in that the surgical access system 6 may be particularlysuited for establishing an operative corridor to an intervertebraltarget site in a postero-lateral, trans-psoas fashion so as to avoid thebony posterior elements of the spinal column.

FIGS. 59-60 are exemplary screen displays (to be shown on the display190) illustrating one embodiment of the nerve direction feature of themonitoring system shown and described with reference to FIG. 57-58.These screen displays are intended to communicate a variety ofinformation to the surgeon in an easy-to-interpret fashion. Thisinformation may include, but is not necessarily limited to, a display ofthe function 230 (in this, case “DIRECTION”), a graphical representationof a patient 231, the myotome levels being monitored 232, the nerve orgroup associated with a displayed myotome 233, the name of theinstrument being used 234 (in this case, a dilator), the size of theinstrument being used 235, the stimulation threshold current 236, agraphical representation of the instrument being used 237 (in this case,a cross-sectional view of a dilator 8 or 9) to provide a reference pointfrom which to illustrate relative direction of the instrument to thenerve, the stimulation current being applied to the stimulationelectrodes 238, instructions for the user 239 (in this case, “ADVANCE”and/or “HOLD”), and an arrow 240 indicating the direction from theinstrument to a nerve. This information may be communicated in anynumber of suitable fashions, including but not limited to the use ofvisual indicia (such as alpha-numeric characters, light-emittingelements, and/or graphics) and audio communications (such as a speakerelement). Although shown with specific reference to a dilating cannula(such as at 234), it is to be readily appreciated that the presentinvention is deemed to include providing similar information on thedisplay 190 during the use of any or all of the various instrumentsforming the surgical access system 6 of the present invention, includingthe dilation assembly 7 (i.e. the K-wire 42 and dilators 8 and 9) and/orthe retractor blade 12 or the shim elements 22, 25.

As evident from the above discussion and drawings, the present inventionaccomplishes the goal of gaining access a surgical target site in afashion less invasive than traditional “open” surgeries and, moreover,does so in a manner that provides the ability to access such a surgicaltarget site regardless of the neural structures required to be passedthrough (or near) in order to establish an operative corridor to thesurgical target site. The present invention furthermore provides theability to perform neural monitoring in the tissue or regions adjacentthe surgical target site during any procedures performed after theoperative corridor has been established. The surgical access system ofthe present invention can be used in any of a wide variety of surgicalor medical applications, above and beyond the spinal applicationsdiscussed herein. Such spinal applications may include any procedurewherein instruments, devices, implants and/or compounds are to beintroduced into or adjacent the surgical target site, including but notlimited to discectomy, fusion (including PLIF, ALIF, TLIF and any fusioneffectuated via a lateral or far-lateral approach and involving, by wayof example, the introduction and/or removal of bone products (such asallograft or autograft) and/or devices having ceramic, metal and/orplastic construction (such as mesh) and/or compounds such as bonemorphogenic protein), total disc replacement, etc.

Moreover, the surgical access system of the present invention opens thepossibility of accessing an increased number of surgical target sites ina “less invasive” fashion by eliminating or greatly reducing the threatof contacting nerves or neural structures while establishing anoperative corridor through or near tissues containing such nerves orneural structures. In so doing, the surgical access system of thepresent invention represents a significant advancement capable ofimproving patient care (via reduced pain due to “less-invasive” accessand reduced or eliminated risk of neural contact before, during, andafter the establishment of the operative corridor) and lowering healthcare costs (via reduced hospitalization based on “less-invasive” accessand increased number of suitable surgical target sites based on neuralmonitoring). Collectively, these translate into major improvements tothe overall standard of care available to the patient population, bothdomestically and overseas.

What is claimed:
 1. An elongate disposable electrode for insertion intoa surgical retractor blade, the electrode comprising: (a) a proximalend; (b) a distal end; (c) a generally flat electrode body; (d) aconducting trace extending through the electrode body such that thetrace is only exposed at a first exposed area at about the proximal endand at a second exposed area at about the distal end; (e) a pair offlattened wings running along the electrode body between the firstexposed area and the second exposed area, wherein said wings aregenerally coplanar; and (f) a ledge at the distal end, said ledgeextending in a direction generally perpendicular to a plane defining thepair of flattened wings.
 2. The electrode of claim 1, wherein saidelectrode is sterile.
 3. The electrode of claim 1, wherein saidelectrode body is composed of molded plastic.
 4. The electrode of claim1, wherein said electrode body is composed of a dielectric material. 5.The electrode of claim 1, wherein said electrode body is composed ofpolyvinyl chloride (PVC).
 6. The electrode of claim 1, comprising adielectric coating at least partially covering the trace.
 7. Theelectrode of claim 1, wherein said conducting trace is composed of aconductive metal selected from the group consisting of: silver andcopper.
 8. The electrode of claim 1, wherein the first exposed area isgenerally cylindrical.
 9. The electrode of claim 1, wherein the firstexposed area wraps around the circumference of the proximal end of theelectrode.
 10. The electrode of claim 1, wherein the electrode has alongitudinal dimension of at least 20 mm.
 11. The electrode of claim 1,wherein the electrode has a longitudinal dimension of at least 180 mm.12. A method of preparing a surgical retractor blade for use with asurgical access system capable of detecting neural structures byinserting an electrode into an electrode blade, wherein the electrodeblade has an interior surface and an exterior surface, a distal end, anda proximal end, and the electrode blade comprises: an elongate slotextending longitudinally through the electrode blade, and a firstopening along the exterior surface; wherein the electrode is removablycouplable with said electrode blade and configured to be slideablyreceived along the elongate slot, said electrode comprising a proximalend and a distal end; wherein said method comprises sliding theelectrode into the elongate slot until the distal end reaches the firstopening.
 13. The method of claim 12, wherein the electrode comprises:(a) a generally flat electrode body; (b) a conducting trace extendingthrough the electrode body such that the trace is only exposed at afirst exposed area at about the proximal end and at a second exposedarea at about the distal end; (c) a pair of flattened wings runningalong the electrode body between the first exposed area and the secondexposed area, wherein said wings are generally coplanar; and (d) a ledgeat the distal end, said ledge extending in a direction generallyperpendicular to a plane defining the pair of flattened wings.
 14. Themethod of claim 12, wherein said electrode is sterile.
 15. The method ofclaim 12, wherein said electrode is at least partially composed ofmolded plastic.
 16. The method of claim 12, wherein said electrode is atleast partially composed of a dielectric material.
 17. The method ofclaim 12, wherein said electrode is at least partially of polyvinylchloride (PVC).
 18. The method of claim 13, comprising a dielectriccoating at least partially covering the trace.
 19. The method of claim13, wherein said conducting trace is composed of a conductive metalselected from the group consisting of: silver and copper.
 20. The methodof claim 13, wherein the first exposed area is generally cylindrical.21. The method of claim 13, wherein the first exposed area wraps aroundthe circumference of the proximal end of the electrode.
 22. The methodof claim 1, wherein the electrode blade has a longitudinal dimension ofabout 20-180 mm, and the electrode has a longitudinal dimension thatexceeds the longitudinal dimension of the electrode blade.